Caulerpa gets a bad rap for its tendency to reproduce sexually when it undergoes "seasonal changes". These natural cues, primarily a change in photoperiod (daylight hours) cause the caulerpa to shut down and release spores into the water. The water can get quite cloudy and the raid die-off releases bound nutrients and heavy metals. If you keep a steady photoperiod of 16 hours on and 8 hours off, the algae will not reproduce sexually and or crash. The addition of an iron supplement will also boost macro algae growth.
Mixing a DSB and refugium is a bad idea as one requires light and the other competes with photosynthetic organisms. many hobbyists report that he addition of a RDSB has an impact on nitrate levels, but you will find more success stories in discussions of slow flow denitrators, sulphur bead filters, Algae turf scrubbers/refugia, carbon media, and carbon dosing.
The size of a RDSB must also reach a critical mass. I followed a thread her on RC for years on 5 gallon bucket RDSB's. It was an epic thread with page after page of plans for buckets and powerheads. Everyone swapped design ideas and everyone was happy with their handy work but there wasn't a single report of nitrate reduction. I can't say with any certainty that the idea doesn't work, but it was a huge test group with no positive feedback other than the ultimate use of uniseals, maxijets, and old salt buckets.
Water changes are very poplar but they are the least efficient method of nutrient export. Salt and even source water isn't cheap and a 10% water change will reduce the bad stuff by only... you guessed it 10%. If you use a good salt mix it will replace 100% of the missing elements, but only in 10% of the water. The other 90% needs to be supplemented chemically via your method of choice. I'm patient for the curtain rise on that one

What water changes will do is remove the "unknowns" as many people call them. I don't know of any unknowns that cannot be removed through mechanical (socks & cartridges etc.), biological (rocks, sand, algae farming, organisms etc.), chemical (polymers, ion exchange resins, protein skimming, sulphur or carbon beads etc.), or disinfection (UV irradiation & ozone) filtration. I'm not saying water changes are a bad thing, but if you measure the resources used and the amount accomplished, it doesn't measure up to the other weapons in our filtering arsenal.
The original magician of Miracle Mud, Leng Sy, operates his refugium on a 24 hour photoperiod, offering no rest time for photosynthetic respiration. This practice tricks the caulerpa into thinking it is one never ending day so it doesn't reproduce sexually. Leng Sy experiences little or no growth of the algae, at least in his original tank. The caulerpa develops hormonal deficiencies due to the lack of respiration (night/dark period). In doing so you lose the valuable nutrient export associated with the harvesting of macro algae. Once again, this is based on his original system. I haven't heard much about it in the last 15 years so I'm sure he has made some modifications.
Here is a discussion from another forum I found.
http://new.ultimatereef.net/forums/showthread.php?p=1367737
The idea of massive water changes (30% per month), and the harvesting of large volumes of macro algae leaves me to wonder what the value of the mud is? It's like those miracle diet pills they sell where you have to get lots of exercise and eat healthy foods to make them work.
In my opinion, however humble, the macro algae in Leng Sy's systems act as a semi-buoyant biological filter media, similar to the lightweight mud he sells. Sand beds are most efficient on the surface, so adding more surface area improves overall performance. The denitrifying microbes that live on coral tissue live on the branches and leaves of the macro algae as a biofilm (slime coat). The constant farming of algae removes this slime that takes weeks to develop layer by layer.
The other function of a Miracle Mud system is it provides lots of viable sites for benthic invertebrates that polish the water such as worms, barnacles, bivalves, sponges, and tunicates.
Mangroves are not fast growers so they do not directly export significant amounts of nutrients or heavy metals, but they do foster the growth of microbes on their root mass that consume the bad stuff. Like the miracle mud, they also harbour lots of water polishing benthic detrivores.
The most interesting feature of mangrove tress is the tangled web of roots. In orer to get your mangroves to grow "legs" like this, you need to elevate them 4-6" every month or so. This practice simulates the ebb and flow of tidal waters and or heavy rains in mangrove swamps. In nature, the water level drops and the mangrove tree stretches its roots deeper into the water. You will see a change in the colour and texture of the roots as it adapts to the change in water level. The lower root mass is green and smooth and it is adapted to being submerged, while the upper root mass is brown and rough more like traditional bark. The upper "air roots" are more for structure than water collection.
Mangrove trees don't actually require salt water and do quite well in freshwater and soil. Mangroves are able to extract freshwater from saltwater and expel the salt through their leaves. In nature, morning dew and rain washes the salty residue away, but in a home aquarium you need to have one of your staff wipe them with a wet cloth by hand.
Mangrove trees have a high demand for magnesium, so they should be planted in dolomite (calcium magnesium chloride) which is available at your local farm supply store (Ren's Feed Store on Trafalgar in Oakville). You can add some dolomite to your calcium reactor (if you decide to get one) to buffer magnesium, which stabilizes calcium supplementation.